lib: fix config handling

Fixed DebugServer to pass the correct config object to the Session constructor.

Improved error reporting in lib/config.js.
lib: fixed hiding of script files

Modified ScriptFileStorage.findAllApplicationScripts() to exclude files to
hide.

Modified ScriptManager to never hide the main application script file.
README: added FAQ entry for --hidden option

Described what is the format and how to specify the value using
the command-line switch.
Quick fix for properties displayed twice in UI

The upgraded front-end sends two requests to get a list of object properties,
each request asking for a different set of variables. Because our back-end was
ignoring request parameters, the same set of variables was returned twice.

This commit fixes the immediate problem, without providing the full
implementation of the new front-end feature.